Bandpass



Feb. 14, 1956 D. D GR|EG 2,735,073

BANDPASS FILTER SYSTEM Filed Aug. 2, 1952 l a z N= ODD INTEGER 474 5 I Z R A Z J /0 7 7 7 /a a/Qgfi ,4

Z /a 22 23 L;- 57 13 5 Ila 5 /3 l9 A/Jl INVENTOR J F 00mm 0 45m;

ATTORNEY probe system including probes 7 and 8 extending through layer 14 and openings 10 and 10a in wall 13 to couple signal energy from filter 9, establishing the desired bypass communication whereby easy tuning of the circuitry associated with said filter in a'microwave system may be achieved. This small variation in the width of the line conductor may produce variations in the characteristic impedance of transmission line 11 as desired, but the field distribution with respect to the ground conductor is not materially disturbed, or if disturbed it quickly stabilizes itself to provide the desired by-pass communication under the new line conductor conditions.

The means to control the bypass communication shown in Figs. 2 and 3 comprises a pivoted segment 17 substantially identical to the line conductor 12, the segment being pivoted as indicated bypin 18 which may comprise conductive metal or dielectric material. Where the pin 18 is of conductive material it is made short so as not to extend to the wall 13. By keeping such a pin small in diameter and spaced from wall 13 it has substantially no eifect on the flow of high frequency energy along the line. For other types of switches that may be used as the means to control the by-pass communication reference may be made to the aforementioned copending application, Serial No. 280,106.

The location of switch 17 in relation to the coupling probes 7 and 8 is important herein to provide proper impedance terminations for the probes when the switch is in open position. To assure in effect a shortcircuit condition at the probes it is necessary that the open terminals of the switch be located a distance from each of the probes 7 and 8, where N is equal to an odd integer. Preferably, the opening in conductor 12 caused by switch 17 occurs one quarter wavelength from either one of the probes while the remaining probe may be located any odd number of quarter wavelengths from the switch.

Employing the bypass means as herein illustrated the probes 7 and 8 remain in the path of signal propagation at all times with the bypass communication being controlled by means of switch 17, which when opened produces an effective short at the probes. By leaving the coupling probes in the path of signal energy during opening of the switch 17 does not disturbappreciably any alignment and tuning accomplished during by-pass communication.

Referring to Fig. 4, a shorting means 19, shown herein to be a screw, may replace switch 17 of Figs. 2 and 3 to provide means for controlling the bypass communica tion. Line conductor 12:: and dielectric material 1% are provided with an aperture 20 which may be threaded for reception of shorting means 19. A stiffening member 21 is also provided contiguous to conductor 12a to reduce possible stresses set up in conductor 12a upon transverse movement of shorting means 19. To interrupt by-pass communication shorting means 19 is moved transversely into contact with ground conductor 13a, thereby shorting line conductor 12a. The shorting means 19 is located a distance from each of probes 7a and 8a, where N is equal to an integer, thus providing proper impedance termination for each probe when the shorting means is in the interruption position to introduce the selectivity characteristics of the filter to the system. The location of shorting means from the probes as outlined hereinabove assures an effective short circuit at the probes. Preferably, the short in conductor 12:: caused by shorting means 19 when in its interruption position occurs one half wavelengthffrom either of the probes while the remaining probe may be located any integral number of one half wavelength from the shorting means. Instead of a shorting screw other shorting arrangements maybe provided, such a shorting arrangement, for example, may comprise a key slidable in a keyway formed in the dielectric transversely of the line conductor whereby the key may be moved to a shorting position between the conductors.

Fig. 5 illustrates an attenuator which may replace switch 17 of Figs. 2 and 3 to provide means to control the by-pass communication. Line conductor 12b will be continuous from one coupling probe to the other in this embodiment. Pivoted segment 22 comprises a lossy conductive material, the segment being pivoted by means of pin 23. To disrupt the by-pass communication attenuator portion 22 is pivoted to the position shown by the dotted lines such that the by-pass energy will be absorbed by said attenuator. When employing this by-pass means the coupling probes extend into the path of the signal energy just sufficient to by-pass the minimum amount of energy required to align and tune preliminarily the circuitry as sociated with a given preselector filter in a microwave system. Upon termination of the by-pass communication by means of attenuator 22 a certain amount of energy will be absorbed by said attenuator. This absorbed energy will substantially equal that energy previously present in the by-pass communication. Therefore, when the selectivity characteristics of the filter is introduced to the system by means of attenuator 22 the amplitude of the signal passing through the system will decrease by an amount equal to the energy absorbed by the attenuator 22.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. A microwave bandpass filter system comprising a filter which includes a section of a waveguide, signal input means and signal output means for said filter, and a transmission line to provide a filter bypass communication between said signal input means and said signal output means to bypass a portion of the signal energy about said filter to reduce the selectivity of said filter during tuning adjustments, and means to interrupt the bypass communication after tuning to introduce the selectivity characteristics of said filter, said transmission line including first and second conductors disposed in spaced substantially parallel relation 21 small fraction of a quarter wavelength apart wherein the second of said conductors comprises a wall of said waveguide section.

2. A filter according to claim 1, wherein said interrupting means comprises a segment of said first conductor movable between line opening and closing positions.

3. A filter according to claim 1, wherein said interrupting means comprises a portion of said first conducto pivoted at one end thereof.

4. A filter according to claim 3, wherein said interrupting means is located an odd number of quarter wavelengths away from each of said input means and said output means.

5. A filter according to claim 1, wherein said interrupting means comprises an attenuator including a body of lossy material with at least a section of said body being adapted to be disposed in the electromagnetic path of said transmission line.

6. A filter according to claim 5, wherein in at least a part of said body is disposed closely adjacent one of said conductors.

7. A filter according to claim 6, wherein said body is pivoted at one end for movement relative said one of the conductors.

8. A filter according to claim 1, wherein said interrupting means comprises a body of lossy material and means pivotally supporting said body on said wall for movement relative said first conductor.

9. A filter according to claim 1, wherein said interrupting means comprises a line shorting element and means for moving said element into conductive relation with respect to both said conductors.

10. A filter according to claim 9, wherein said interrupting means is located an integral number of half wavelengths away from each of said input means and said output means.

11. A combination filter and bypass system comprising a filter having a housing of conductive material, said housing having a signal input at one end thereof and a signal output at the other end thereof, a wall of said housing having an opening therethrough adjacent the input end of said housing and another opening adjacent the output end of said housing, a conductor disposed in spaced parallel relation to said wall and extending between said openings, and means coupling said conductor through said openings to the interior of said housing to form a bypass communication directly between the input and output ends of said filter.

12. A system according to claim 11, wherein said conductor is ribbon shaped and has the end portions thereof tapered, and the means for coupling said conductor to the interior of said housing includes a probe disposed in each of said openings in conductive relation to the tapered end portion of said ribbon conductor.

13. A system according to claim 11, wherein a layer of dielectric material is disposed between said ribbon conductor and said wall to maintain said ribbon spaced a small fraction of a quarter wavelength from said wall.

14. A system according to claim 11, wherein said conductor is provided with a section movable between conductor closing and conductor opening positions, said section being located a distance from said coupling means to provide when in open position an effective short at said coupling means.

15. A system according to claim 11, wherein said conductor has associated therewith a body of lossy material movable relative thereto for attentuating the line when it is desirable to interrupt the bypass communication.

16. A system according to claim 11, wherein said conductor is provided with a conductive member movable between bypass communication position and bypass interrupting position, said member being located at a distance from said coupling means to provide when in its interrupting position an effective short at said coupling means.

References Cited in the file of this patent UNITED STATES PATENTS 2,272,589 Steinmetz Feb. 10, 1942 2,390,768 Austin Dec. 11, 1945 2,519,524 Wheeler Aug. 22, 1950 2,611,822 Bliss Sept. 23, 1952 

